人工鱼礁投放对小窑湾海域水动力及水体交换影响的数值模拟

Numerical simulation of effects of artificial reef on hydrodynamics and water exchange in Xiaoyao Bay

为探究大连小窑湾海域人工鱼礁布设后对周围海域水动力特性及水体交换能力的影响,基于非结构化三角形网格的MIKE3河口与海岸模型,对大连小窑湾海域进行数值模拟,模拟结果与实测数据吻合良好,说明构建的模型合理可靠。研究表明:1)鱼礁布设后,位于鱼礁布设点上的测点因水深减小,流速增加,远离礁区海域测点的流速变化较小,鱼礁区迎流面海域出现上升流,背流面出现下降流,底层海域的上升流效应较表层海域显著;2)人工鱼礁的投放会引起局部流场发生变化,受鱼礁堆阻流作用影响,鱼礁堆迎流面、背流面海域流速减小,主流轴两侧流速增加,鱼礁堆附近海域的流速呈缓急相间分布;3)人工鱼礁投放后,小窑湾湾顶、湾中的水体半交换期缩短,湾口附近海域水体交换能力变化较小,小窑湾整体海域水体交换率略有增加。研究结果可为人工鱼礁合理布局以及规范工程建设提供理论指导。

Artificial reefs can change the characteristics of tide currents in surrounding waters and provide an ideal living environment for marine organisms.It is necessary to study the effect of artificial reefs on flow field and water exchange capacity after the construction.Xiaoyao Bay is a semienclosed bay in the Yellow Sea with regular semidiurnal tide type.In recent years,site selection and planning layout of artificial reefs have been actively carried out in Xiaoyao Bay.This study used MIKE3 estuarine and coastal model to investigate the effects of artificial reef construction on the hydrodynamic characteristics and water exchange capacity in Xiaoyao Bay.This model used the unstructured triangular mesh and finite volume method.We carried out a series of numerical simulation scenarios in the study area before and after artificial reef construction.The simulated results were in good agreement with the measured data,indicating that the present model was reasonable and reliable.The study results showed that:Firstly,after the construction of artificial reefs the current velocities above the region of artificial reefs increased because of the decrease of water depth,and the current velocities changed slightly in areas far from artificial reefs.The upwelling was generated in inflow area of artificial reefs,and the downwelling was generated in downstream area of artificial reefs respectively,where the upwelling effect in bottom layer was more significant than that in surface layer.Secondly,from the horizontal scale,the construction of artificial reefs caused significant changes of flow field in the local areas,the velocities in inflow and downstream areas near artificial reefs decreased,and the velocities of two sides of the mainstream axis increased due to the block of artificial reefs,and the alternately slow and fast distribution for flow velocities occurred around reef stacks.During fast flood tide,the maximum increase of surface velocity was 0.14 m·s^(-1) and the maximum increase of bottom velocity was 0.049 m·s^(-1),while the velocity changes for surface and bottom layers were similar.The velocity changes for surface and bottom layers caused by the construction of artificial reefs were mainly distributed within the domain of 2 km near the reef placement area,and the flow velocity changed slightly in sea areas far away from the artificial reef area.Thirdly,the water halfexchange periods in the top and middle parts of Xiaoyao Bay were shortened after artificial reef construction,the sea water exchange capacity changed slightly near the mouth of the bay,and the overall sea water exchange capacity was slightly enhanced,indicating that artificial reef construction had less impact on water exchange capacity in Xiaoyao Bay.The study results can provide theoretical guidance for the reasonable layout and construction of artificial reef engineering.In generally,the construction of artificial reefs will not only affect the tidal motion and water exchange characteristics in the coastal waters,but also affect the process of sediment transport,and change the state of siltation of seabed on the bottom of artificial reefs,or even the evolution of the seabed geomorphology and offshore topography.Therefore,sediment erosion and deposition near the artificial reefs should be studied in future work to ensure the stable state of artificial reef after its construction in Xiaoyao Bay.